The atomic force microscope is widely used for nanoscale surface characterization. There is an increasing interest in its use for mapping of material specific surface properties. Quasistatic methods, such as nanoindentation, and several dynamic methods, such as ultrasonic force microscopy, pulsed-force microscopy, and force modulation microscopy, have been developed for local stiffness measurements. These techniques generally suffer from low operational speeds and require large forces applied to the surface under test, limiting their use on soft materials such as biological samples.
Tapping-mode atomic force microscopy (AFM) is an often-used operational mode, which is particularly useful for soft samples. In tapping-mode, phase information and higher harmonic signals can be used to obtain nanoscale maps of material characteristics. Measurement of tip-sample interaction forces is a more direct method for material characterization. Recently, measurements of tip-sample interaction have been demonstrated by specially designed probes. However, these approaches have included structural components that generally limit the ability to detect and/or characterize surfaces and, in some instances, the ability to characterize soft surfaces. Moreover, these approaches have been limited in the resolution that can be obtained, due to characteristics of the cantilevers and related structures that are used to interact with samples.
These and other issues have presented challenges to the implementation and design of AFM cantilevers and AFM microscopes.